richardson



(No Model.)

'0. H. RICHARDSON. MEANS FOR REGULATING ELEOTRIG MOTORS.

No. 501,961. Patented July 25,1898.

WITNESSES INVENTOR JAMAO EW ma Jb M 7 UNITED STATES PATENT Prion.

CHARLES H. RICHARDSON, OE PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO THE S. S. WVHITE DENTAL MANUFACTURING COMPANY, OF SAME PLACE.

MEANS FOR REGULATING ELECTRIC MOTORS.

SPECIFICATION forming part of Letters Patent No. 501,961, dated July 25, 1893.

Application filed January 16, 1893. Serial NJ1581497- No model.)

To all whom it may concern: the motor armature tends to reduce its speed Be it known that I, CHARLES H. RIOHARD- below the point determined by the fan or fan SON, of the city and county of Philadelphia, blades and this extra reduction in speed tends in the State of Pennsylvania, have invented a to rapidly reduce the resistance (mechanical) certain new and useful Improvementin Means of the fan or fan blades thus taking much less for Regulating Electric Motors, of which the power to drive them than before, and this following is a specification. power saved from the fan is delivered to the Myinvention relates to an improvement esexternal work, thus giving more power to it pecially applicable to use in regulating elecand keeping the speed more nearly constant 1o tric motorsforreducingspeed and at thesame at the predetermined reduced speed than time retaining the power or torque of the arwould be the case with a friction brake. In mature shaft at full or nearly full amount. the friction brake the back pull per revolu- In an electric motor it is sometimes very tion is the same or nearly so at all speeds and desirable to obtain a speed much lower than on putting on extra external work no power 15 the full speed and at the same time preserve is given up by the brake to the external work, as much as possible of the full amount of which is the defect mentioned as requiring torque or pull on the armature shaft. It is further explanation. well known that if this is attempted to be My object is to attain the same results as done by putting in resistance in series or given by the fan or fan blades, by electrical 2o shunt with the motor, the speed is reduced as means. resistance is added,but soon apoint is reached To attain the desired end by means under where the torque or pull of the armature is the control of the operator, I make the armarapidly reduced and this reduction in torque ture core of the motorin the usual laminated or pull eventually reaches a point where little form, and wind on the usual coils connected 25 work can be obtained from the motor. in the usual way to an ordinary commutator;

It is known that there can be put afriction besides these I wind on the motor armature brake on the armature shaft, and thus slow core an extra set of coils constituting generit down either working directly on the main ating coils electrically separate from the first supply of current or with a resistance interset, and connected to their own commutator,

3o posed; but this method produces the same which may be so arranged as to give either back pull on the shaft or armature for each alternate or direct currents as desired. Prorevolution thereof, whether the motor armavision is made for electrically connecting the ture is running fast or slow and develops cerbrushes or collectors on the commutator of tain disadvantages when the motor is perthe extra or generating coils with a resist- 35 forming external Work which willbe explained ance capable of being Varied and thus varyfarther on. An air fan, or fan blades iming the speed below full speed, by putting mersed in some liquid could be placed on the more or less work on the motor. Instead of armature shaft of the motor or connected winding the extra or generating coils on the mechanically to be revolved by it, and the fan motor armature core, they can be wound on 0 or fan blades would reduce the speed of the a separate core revolving in the same or anmotor armature, to a degree depending on other field and mechanically connected to their size and the angle at which they are set and driven by the armature shaft of the moto the air or liquid. This method of regulator whose rate of speed is to be varied. In tion has the advantage, that as the speed is this form of electrical speed reducer any 45 decreased by some external work below the extra reduction of speed due to external work, 5 point pie-determined by the fan resistance, reduces the current in the extra or generatthe resistance (mechanical) of the fan blades ing coils and their closed circuit through the rapidly decreases, in fact in a ratio someresistance, thus taking less power for the where near the square of the speed. Obspeed reducer, which power is given to the 50 viously the external work which is put upon the external work, and besides obtaining a I00 strong pull on the motor shaft at slow speed the slow speed is maintained more nearly constant.

In the accompanying drawings which show suitable organizations for carrying out my invention in several equivalent ways, Figure 1 is a side elevation showing a form of apparatus in which the generating coils revolving in their own separate field are driven by a belt from the shaft of the motor whose speed is to be reduced. Fig. 2 is a view partly in plan and partly in horizontal section of a form of apparatus in which the generating coils revolve in their own separate field and are mounted rigidly on the elongated shaft of the motor armature. Fig. 3 is a view substantially similar to Fig. 2 except that the generating coils and the motor armature both rotate in the same magnetic field. Fig. 4: represents partly in plan and partly in horizontal section a form of apparatus in which the generating coils are wound upon the same core as the motor armature coils from which they are electrically separated. Fig.5 is a view in end elevation of a portion of the apparatus shown by Fig. 4.

Referring now to Fig. 1, a suitable motor A is shown as provided with a pulley a on the armature shaft from which passes a belt B to the external work to be done, such for instance as the actuation of a rotary dental tool. A second pulley b on the motor armature shaft, actuates a belt 0 for driving a pulley c on the armature shaft of a set of generating coils D. The motor armature and the generating coils armature revolve in their respective fields E E when the motor is connected to the electrical source of supply. The generating coils are adapted to be pntin or out of circuit with a variable resistance F of well known kind. The connection of this resistance with the generating coils is by means of brushes and a commutator Gin obvious way.

In Fig. 2 the armatures of the motor coils and the generating coils are rigidly connected to a common shaft, and revolve in their separate fields E E. The generating coils D are adapted to be connected with the resistance F as before.

Figs. 3 shows, with one exception, substantially the same organization as Fig. 2, the exception being that both the motor armature and the generating coils armature revolve in the one field E.

Figs. t and 5 show the motor coils, and the generating coils D all wound on one armature core, the two sets of coils revolving in the one field E,and the resistance being provided as before.

In lieu of the employment of a belt connection between the armature shaft of the motor and the generating coils armature, toothed gearing may be employed in suitable way.

In operation the supply current is turned into the motor to give it the full speed. A suitable switch operated resistance It in the supply circuit may serve to produce the first reduction in speed. To still further reduce the speed of the motor, the variable resistance is thrown into electrical connection with the generating coils, and the result is that the electric current in the generating coils takes power from the motor and slows it down without reducing its pull or torque to any appreciable extent, while by this resistance speed may be reduced as desired, by increasing the amount of current produced in the generating coils. As will be obvious the counter electro-motive force in the motor is lessened in proportion to the reduction in speed, thus allowing more current to pass through the motor armature at slow speed than at high speed.

I claim as my invention The combination of an electric motor for doing external mechanical work, generating coils electrically separate from the motor armature and mechanically connected with and driven by the motor shaft, and a variable resistance in circuit with the generating coils, whereby provision is made for controlling the speed of the motor armature shaft while maintaining nearly constant the torque or pull thereon at any given speed determined by the adjustment of the resistance, substantially as set forth.

In testimony whereof I have hereunto subscribed my name.

OHARLES II. RICHARDSON.

Vitnesses:

J. A. B. WILLIAMs, R0131". E. GORDON. 

